Studies of radiatively important clouds with 8-millimeter-wavelength Doppler radar

Uncertainty about the physical properties of clouds is recognized as a major reason for the failure of general circulation models (GCM) to correctly simulate climate. To address this problem, NOAA's Environmental Technology Laboratory (ETL) has developed a versatile, cloud-sensing Doppler radar along with new remote-sensing techniques to observe bulk and microphysical properties of cirrus and marine stratus clouds. The 35-GHz (8.6 mm wavelength) polarimetric Doppler radar is stable enough to observe vertical velocities of cloud particles to better than 5 cm s/sup -1/ and to detect echoes as weak as -50 dBZ at a range of 1 km. It has been used recently for cirrus cloud observations. A multiple-sensor technique utilizing measurements from this radar and a vertically pointing IR radiometer has been developed from these datasets to determine ice water path and vertically integrated ice crystal size and concentration. An extension of this technique has been developed to estimate profiles of characteristic ice particle size and concentration. Similarly for non-precipitating warm stratus clouds, vertical profiles of cloud droplet size distributions have been estimated with this radar along with a three-channel microwave radiometer. Doppler spectral moments have been utilized to estimate size distributions in drizzle. In situations where drizzle is absent, Doppler velocity measurements have been used to examine the diurnal variations of turbulence within stratus clouds to infer the importance of radiatively induced mixing at cloud top. Cloud boundary statistics have been examined with both datasets. These observations show the widespread occurrence of multiply layered cloud systems which may have serious implications for the retrieval of cloud information from satellites.<
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